1. Field of the Invention
The present invention generally relates to a burst phase correcting circuit. More specifically, the present invention relates to a burst phase correcting circuit which performs correction of a phase of a chrominance signal on the basis of a phase reference signal in a video tape recorder, video disk player, television receiver and etc.
2. Description of the Prior Art
In a video tape recorder, video disk player and etc., a hue jitter due to instability of a servo circuit or the like occurs. In order to remove such a jitter component, a phase of a color burst included in a reproduced chrominance signal may be corrected. One example of such a kind of burst phase correcting circuit is disclosed in, for example, Japanese Patent Application Laying-Open No. 2-19096 [H04N 9/83] laid-open on Jan. 23, 1990. In this prior art shown in FIG. 1, a chrominance signal is inputted to a terminal 1, and the chrominance signal is applied to an automatic phase control circuit 2. In the automatic phase control circuit 2, a phase of the chrominance signal is controlled on the basis of a horizontal synchronization signal H.sub.sync and a reference frequency signal f.sub.ref from an oscillator 4. An output from the automatic phase control circuit 2 is withdrawn at a terminal 9 through a phase adjustment circuit 3.
On the other hand, an output signal of the automatic phase control circuit 2 is also applied to one input of a phase-comparator 6 included in a control signal generating circuit 5, and the above described reference frequency signal f.sub.ref is applied to the other input of the phase-comparator 6. Accordingly, the phase-comparator 6 compares phases of the two signals with each other, and outputs a pulse having a width according to a phase difference of the both signals so as to apply to a low-pass filter 8 via a gate 7 which is controlled by the horizontal synchronization signal H.sub.sync. Therefore, a control signal having a level according to the phase difference of the both signals is outputted from the low-pass filter 8 and applied to the aforementioned phase adjustment circuit 3.
In the phase adjustment circuit 3, the phase of the chrominance signal outputted from the automatic phase control circuit 2 is further finely adjusted in accordance with the control signal. Therefore, at the terminal 9, a chrominance signal having a phase which is controlled by the automatic phase control circuit 2 and further finely adjusted by the phase adjustment circuit 3 is outputted. Therefore, even if a jitter component is included in the reproduced chrominance signal, the jitter component can be removed.
Since the above described prior art is a feed forward system, it is necessary to provide a level adjustment circuit (not shown) between the low-pass filter 8 and the phase adjustment circuit 3, for example, and to produce a control signal which is coincident with a characteristic of a control signal level-phase of the phase adjustment circuit 3 on the basis of an output of the low-pass filter 8. Such a kind of level adjustment circuit is complex and high cost.
Therefore, it can be considered that in the prior art shown in FIG. 1, a circuit of a feed-back system in which an output of the phase adjustment circuit 3 is applied to the one input of the phase-comparator 6 instead of the output of the automatic phase control circuit 2 is constructed. If the circuit is a feed-back system, the above described level adjustment circuit becomes unnecessary, and therefore, the circuit becomes simple and low cost.
However, in a case where a circuit of a feed-back system is constructed by applying the above described modification to the prior art shown in FIG. 1, it takes a long time until a phase of the chrominance signal becomes to be synchronized. That is, a pull-in time becomes long. Then, in order to make the pull-in time short, a large direct current component must be fed-back. However, in such a case, a phase-locked loop becomes unstable and, in an extreme case, the prior art becomes not to function as a phase correcting circuit.